1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and method for recording broadcasting programs; and, more particularly, to an apparatus and method for recording broadcasting programs using partial encryption.
2. Description of Related Art
Various apparatuses and methods have been introduced for recording broadcasting programs. Among them, a time shifting method and a personal video recorder (PVR) have been widely known. The time shifting method enables a user to record a predetermined broadcasting program in real time and watch the recorded broadcasting program in later. The personal video recorder (PVR) enables a user to record a predetermined broadcasting program at a desired time through reservation. Then, the user can playback the recorded program at any time using the PVR. These methods allow a user to record desired broadcasting programs without additional cost.
A cable broadcasting set top box (STB) employs a local scrambling encryption method for supporting a PVR function. However, a terrestrial broadcasting STB employs a different type of encryption method for supporting a PVR function.
FIG. 1 is a diagram showing an Advanced Television Systems Committee Common Scrambling Algorithm (ATSC CSA) defined as an encryption method in an ATSC standard.
As shown in FIG. 1, the ATSC standard defines a TS packet based encryption method. Particularly, the ATSC CSA of FIG. 1 introduces a block based encryption method that encrypts only predetermined parts of TS packet except a headers and adaptation field. The other encryption methods also introduce a packet based encryption method similar to the encryption method shown in FIG. 1.
The ATSC CSA of FIG. 1 does not cause any technical problems when a personal video recorder (PVR) function is supported through an individual encryption module using a smart card or when a chipset supports a PVR function. However, when a PVR function is used through the same processor equipped in a set-top box (STB) or in a TV set, the ATSC CSA may cause the following problems. For example, in case of a STB having a 300 MIPS (million instructions per second) processor, a processing power of 150 to 200 MIPS is required for encrypting a high definition (HD) broadcasting program. Accordingly, a packet loss problem may occur during encryption when a user wants to watch and record the HD broadcasting program at the same time.
In order to reduce a processing amount of encryption, a partial encryption method was introduced as shown in FIG. 2. As the partial encryption method, various methods have been also introduced such as a partial encryption method for selectively encoding AC components and DC components of a predetermined broadcasting program, a partial encryption method for encoding a header of video components, a motion vector (MV) and a variable length code, a macro block based scrambling encryption method, and a 8×8 block based scrambling encryption method.
However, these partial encryption methods require decoder level analysis, not packet level analysis. Accordingly, the partial encryption methods have to select a range of blocks or packets to be encrypted. This is such a drawback of the partial encryption method.
Further, the partial encryption method is not compatible with a scrambling/encryption standard method defined in a broadcasting standard. Therefore, a device employing the typical partial encryption method cannot be compatible with other devices.
Moreover, the typical partial encryption method was designed to properly work only in an environment guaranteeing a certain level of encryption performance. Accordingly, an encryption process may be interrupted when the certain level encryption performance is disturbed by outputting images for a user, inputting/outputting data into/from a hard disk, and interruptions from an external device. As a result, encrypted or stored packets may be lost.